The invention concerns a method for propulsion regulation of an automobile and more particularly a method for preventing spinning of the driven wheels, as well as an arrangement for execution of the method.
In view of the fact that in recent years considerable and successful efforts have been made to create devices which prevent the locking of vehicle wheels on braking (anti-locking systems, automatic locking prevention), it has become increasingly desirable on propulsion of the vehicle, to cause to act on the vehicle wheels only propulsion moments of such a magnitude that the adherence between the wheel and the roadway is not lost if at all possible, i.e., that the wheels do not spin, in that spinning of the wheel causes either a loss of traction (acceleration) or loss of driving stability, depending on the circumstances.
Contrary to systems for regulation of brake slip-page which as special accessories in passenger cars and in small series have been found to be useful in practice, arrangements for propulsion regulation, i.e., for regulation of propulsion slippage, are essentially still in their experimental or pilot stage.
In accordance with known devices for propulsion regulation of automobiles (e.g., as per DEP No. 3,127,302; DE-OS No. 3,205,627 and DE-OS No. 3,331,297) rotational speed sensors detect the rotational speed of the driven as well as the non-driven wheels and the slip of the driven wheels is determined on the basis of the ratio between the rotational speed of the driven and the non-driven wheels by means of digital or analog electronic circuit units. These slip values are compared with preset maximum slip values, i.e., limit or threshold values. If the limit or threshold values are exceeded, control signals are generated which, depending on whether the slip exceeds the preset limit or threshold value of only one or both driven wheels of an axle, cause the braking of only one driven wheel or the braking of both driven wheels or also only or simultaneously a reduction of the engine torque, e.g., through reduction of the fuel delivery.
Methods are also known (e.g., from DEP No. 3,127,302, DE-OS No. 3,331,297) for determining, with the help of differential stages and on the basis of the detected rotational speed, the angular acceleration of the driven wheels and comparing the same with preset limit or threshold values. As soon as the angular acceleration of the driven wheels exceeds the threshold value, the (acceleration) control signal is generated which in conjunction with the aforementioned (slip) control signal is utilized to influence the control of the engine as well as of the brakes of the driven wheels.
The known arrangements operate in a manner such that values determined on the basis of rotational speeds are compared with threshold values and an exceeding of such threshold values results in that the brake pressure of the wheel brakes associated with one or both spinning driven and driving wheels is built up in a preset manner and/or the fuel delivery or the ignition of the driving engine is modified, likewise in a preset manner, in each case until the spinning of the driven wheel or wheels is eliminated.
In case of these known arrangements we are dealing basically with a regulation in the manner of an antilocking system regulation algorithm with a reversed algebraic sign whereby when a defined angular acceleration or a defined slippage value is exceeded, the propulsion moment on the driving wheels is reduced until (through braking or reduction of fuel delivery) the propulsion slippage has safely become sufficiently small so that subsequently, the reduction can be eliminated until the angular acceleration or the slip value again exceeds the preset threshold value. It is true that this manner of regulation is suitable to constantly utilize the traction of the wheel in the vicinity of the optimal friction coefficient but it is by nature not free from oscillations and thus relatively uncomfortable.
The theoretically simplest regulation algorithm would consist in that the rotational speed of the driven wheels would attain a somewhat higher value than that of the non-driven wheels, whereby the difference between the two speeds would have to be chosen in such a manner that a sufficiently large propulsion slip would be ensured on the driving wheels. But in order to ensure non-oscillating control, such a regulation would necessitate extremely rapid control or correcting elements. Constructions of brake pressure control elements and servo throttle valves deemed suitable in this sense would necessitate an effort which would have to be deemed uneconomical, however.